1. Field of the Invention
The present invention relates to an ink container, and an ink jet head unit which includes the ink container. More particularly, the present invention pertains to an ink container which accommodates an absorber improved so that it assures stable ink supply, an ink jet unit employing such a container, and an ink jet apparatus in which can be mounted in such an ink jet unit.
2. Description of the Related Art
In recent years, ink jet head units in which an ink jet head portion and an ink tank portion are formed as one unit have been drawing attention as the recording unit employed in ink jet recording apparatuses. In such an ink jet head unit, the ink tank portion and a common liquid chamber of the head portion are coupled to each other through an ink supply passage. The ink supply passage is provided with a filter for trapping dust in the supplied ink.
In ink jet type recording, the fixing property of the ink attached to the recording paper is in general one element which determines the printing quality. Ink having a low surface tension fixes fast and does not spread readily, and therefore can be effectively utilized in ink jet recording apparatus, particularly, in color ink jet recording apparatus. However, ink having a low surface tension has a tendency to reduce the quality of printed characters. Particularly, application of black ink having a low surface tension is undesirable. Hence, it has been proposed to use a combination of black ink having a relatively high surface tension and inks of other colors having low surface tensions so as to obtain color images having an improved quality of black characters and no blur.
However, ink having a low surface tension readily bubbles, and the flow thereof is readily interrupted while flowing through the passage for ink supply. Accordingly, air may be taken into the ink tank of the ink jet recording head from a contact surface between the filter and the absorber, resulting in the generation of bubbles in the ink supply passage, the common liquid chamber or the liquid passage. Consequently, non-discharge of the ink may occur or discharge of the ink may be interrupted. Also, the amount of ink which can be used up from the ink tank may be reduced.
The following measures have been taken to improve ink supply properties.
(a) The average pore size of the absorber has been reduced stepwise toward the part of the ink supply passage. PA0 (b) An absorber having a uniform average pore size is inserted into an ink tank whose inner diameter is reduced gradually toward the ink supply port so as to achieve apparent and gradual reduction in the average pore size of the absorber. PA0 (c) A plurality of absorbers having different average pore sizes are employed so as to acheive gradual reduction in the average pore size of the absorber toward the ink supply port.
However, the structure itemized (a) is difficult and expensive to manufacture, and the use thereof in inexpensive ink jet head units is therefore difficult. In the structure itemized (b), since a reduction in the average pore size of the absorber in the ink tank toward the ink supply port is achieved when the absorber is inserted in the ink tank, the pore size may vary locally, making the density of the ink in the ink tank vary. This makes smooth flow of the ink in the absorber impossible, and makes the ink supply interrupted.
In the structure itemized (c), since an absorber having a small average pore size is employed, the amount of ink (ink gross) retained in the absorber is reduced.
In color recording which employs different inks, a plurality of inks having different surface tensions are contained in the ink tanks. In that case, if the average pipe (pore) diameter and wetting angle of the absorber with respect to the ink are equal in each ink tank, since the capillary force of the ink differs in each color, gas may be taken in from the contact surface between the filter and the absorber for the ink having a small capillary force when the inks of all the colors are sucked at the same time.